[varjag]

Landline phones (pre-ISDN) can get their power from the network, thus mitigating one failure vector.

Also, it is much cheaper to provide enough cable than radio transceivers. Thus mobile networks nearly always run close to full capacity... ever had "network busy" on your phone when dialing in a downtown? So they are easily overwhelmed in emergencies. With landline, in contrast, you always have the line, so it is mostly a matter of installing big enough BX station.